RPM fluctuating at all times BUT idle speed

[jimmyducati]

I just replaced the vent purge solenoid and it fixed the stumble at idle and the fuel tank vent issue..
Now I have a new problem!

Pretty much anytime the car is moving forward (with few exceptions that don't really follow a rhyme or reason) the RPM is fluctuating, rising and falling approximately 25-50 RPM about twice per second. Its just enough to be able to hear the engine surge, feel it in the seat and see the tach jump. It is also stumbling slightly anytime I give it a little bit of gas, but not enough to downshift.

Its not throwing any DTC codes and the fuel mileage hasn't changed much, I assume its a sensor or something that is on its way out.. Any ideas on what to start with??

 

[SHOdded]

So the engine is actually surging, probably not a torque converter issue.  Are you datalogging with Torque Pro or Forscan?  I would post those logs, because it makes it a lot easier to figure out what might be happening.  Could be wastegate issue, or it could be a throttle body (motor/sensor) issue.  Have you cleaned the MAP sensors, checked the air filter, the intercooler, turbo piping for leaks, ...?

 

[jimmyducati]

Ya its picking up and dropping 25-50 rpm about twice a second. Even does it on a flat road with the cruse set. I can put it in manual and increase the rpm's and it calms down for a bit, but the surging eventually comes back unless the engine is under a load greater than just maintaining speed.

I looked over all of the pipes yesterday, changed the oil and installed the solenoid on the Evap system under the car. I also got a new set of tunes from LMS, my alky/meth pump stopped working so I needed a catless 3bar tune to run until I get the meth working again. The surging was happening yesterday before I installed the new tunes though. I have the torque app, ill try to get a log recorded on my ride home in the morning.. Hope its not a trans/torque converter issue!! The PTO gets the gear oil changed every other oil change, so its not likely that its the culprit. I will also check the trans fluid level before heading out in the morning, cross that off the list.

 

[jimmyducati]

I have downloaded and FORScan and my wifi ELM reader just showed up.. There are quite a few more PID's possible to log than in the torque app, what PID's do you guys think you might need to see in order to diagnose this stumbling/surging problem?

 

[derfdog15]

I would log as many sensor PIDs as it will let you, with regards to speed control sensors (Throttle, MAP, etc.) as well as engine speed, load, vehicle speed, and possibly a few extras if you have space/bandwidth to do so..

 

[SHOdded]

Take a look at Fomoco's torque layouts, that should help.  Also pick any of the numerous sct logs of late, they have what you are looking for.  Lambda, fuel trim, hpfp fuel pressure, wastegate duty cycle, fuel pump duty cycle/pressure, throttle position, alongside speed, rpm, gear and o2 sendor readings all will be important.

 

[jimmyducati]

Thanks guys! I am driving from Louisville to Ft Campbell this afternoon, should give me plenty of time to get some logs. Hopefully I can catch the shudder and surging in one of them. Its been acting much better since I installed the canister vent solenoid but its still not right.

 

[ZSHO]

Thanks guys! I am driving from Louisville to Ft Campbell this afternoon, should give me plenty of time to get some logs. Hopefully I can catch the shudder and surging in one of them. Its been acting much better since I installed the canister vent solenoid but its still not right.

Glad the vent solenoid helped out a bit but would also try to rule out a pinched fuel line from the canister. Z

 

[jimmyducati]

How could a fuel line have suddenly become pinched? I was able to record atleast one instance of the stumbling and surging on the drive.. now I have to find a way to post a csv file using an iPad....

 

[ZSHO]

How could a fuel line have suddenly become pinched? I was able to record atleast one instance of the stumbling and surging on the drive.. now I have to find a way to post a csv file using an iPad....

Air in the fuel tank/lines which can ultimately cause your vehicle to run rich/lean....Did you also change the valve by the engine bay? Z
Best of luck to ya.

 

[jimmyducati]

I haven't changed the one in the engine bay, did have time before my trip.

Here area  couple logs using FORScan, Ive never used that program to log and don't know if i quite did it correctly. The car was stumbling at idle in the first one and the boost what surging slightly and running generally poorly in the second one.

 

[SHOdded]

Combined and imported into xls for those interested.

 

[jimmyducati]

Vent purge solenoid replaced under the car, Vapor canister purge solenoid replaced, stock tune and 2 bar reinstalled, this piece of **** car still stumbles at idle, the RPM still fluctuates under normal load and still stumbles randomly after upshifting.

I feel like parking it in the back yard and letting the weeds take it over

Seriously at my wits end, it throws zero codes, the data logs look fine, it has brand new O2 sensors, I've tried every tune I can including the latest from LMS... Does anyone have any ideas of what part I should be replacing next?

 

[ajpturbo]

Do you need a strategy update?...put some good trans fluid in? Want to try an ajp turbo tune?

 

[jimmyducati]

Do you need a strategy update?...put some good trans fluid in? Want to try an ajp turbo tune?

I went through the engine bay last week looking for loose boost pipes, air hoses, cleaned the filter, checked the trans fluid (bright red and correct level) and double checked all of the electrical connections. The common knock sensor wire was reinforced last year and is still in good condition.

How does a strategy go bad in a car? What changes in the ECU to cause the motor to run poorly? I didn't get a strategy update that I know of, but I did get new tunes from LMS in an attempt to fix this problem. It I mean, its not like the car has to communicate with peripherals that are constantly updated... its a Taurus, not a laptop! Sorry, that came off like a rant.. Im just frustrated with this.

Im already $$ into a tuner with LMS, so id rather not spend more on software but I do appreciate the offer. I hear great things about your tuning!

 

[ZSHO]

Here's a complete list of TSB on 10-12 SHO.  Z
http://www.ecoboostperformanceforum.com/index.php?topic=496.0

 

[SHOdded]

Any chance the wastegates or their actuating rods are misbehaving?  Have seen this as common issues on the 2.0 ...

 

[pmezo33]

You're 100% sure this isn't torque converter related?  Sounds like a lot of the symptoms i had when my tc went.

 

[jimmyducati]

You're 100% sure this isn't torque converter related?  Sounds like a lot of the symptoms i had when my tc went.

I flushed the trans fluid with a drain and fill 15k miles ago (about 3 oil changes ago) and this problem just started about 1k miles ago. Began as a stumble at idle in traffic that worsened into stalling in traffic. I changed the canister purge solenoid (the one on the side of the canister under the car) and the purge valve that is mounted to the side of the intake last month and the symptoms cleared for maybe 50 miles. It developed into a loss of power under normal driving conditions (very noticeable if I accelerate, but not enough to downshift). While driving at a constant speed, the RPM's may or may not "surge" by aprox. 50 rpm at a constant rate, but the surging would go away if I accelerated WITH a downshift. Sometimes (new symptom) it will act like it has a misfire, rapid violent vibration coming from the engine, but never a misfire DTC.  At WOT, the engine pulls strong, the transmission shifts with authority and all is well. At idle and driving like a sane person, its ****.

All that being said, non of the problems are guaranteed to occur, happens about 30-40% of the time and has zero correlation with the engine being warm/cold or the # of miles driven.

Just out of curiosity, how much was the tc replacement when yours went?

 

[pmezo33]

You're 100% sure this isn't torque converter related?  Sounds like a lot of the symptoms i had when my tc went.

I flushed the trans fluid with a drain and fill 15k miles ago (about 3 oil changes ago) and this problem just started about 1k miles ago. Began as a stumble at idle in traffic that worsened into stalling in traffic. I changed the canister purge solenoid (the one on the side of the canister under the car) and the purge valve that is mounted to the side of the intake last month and the symptoms cleared for maybe 50 miles. It developed into a loss of power under normal driving conditions (very noticeable if I accelerate, but not enough to downshift). While driving at a constant speed, the RPM's may or may not "surge" by aprox. 50 rpm at a constant rate, but the surging would go away if I accelerated WITH a downshift. Sometimes (new symptom) it will act like it has a misfire, rapid violent vibration coming from the engine, but never a misfire DTC.  At WOT, the engine pulls strong, the transmission shifts with authority and all is well. At idle and driving like a sane person, its s***.

All that being said, non of the problems are guaranteed to occur, happens about 30-40% of the time and has zero correlation with the engine being warm/cold or the # of miles driven.

Just out of curiosity, how much was the tc replacement when yours went?

Those are different symptoms that i had with my TC. I got the fluctuating of RPM's when the RPM's were low.  When RPM's were high, it ran smooth.  Happened at all speeds and even in cruise control but was fine at idle.  Did not have any stalling or loss of power.  My issues never felt like a misfire and would not be mistaken for one.  Just a bouncy rpm gauge that you could also feel as it went through the gears. 

I'm not exactly sure what caused my TC to go.  Happened at about 95k miles on my 2010 MKS.  Trans fluid was changed within the year when the symptoms started.  I changed the trans fluid again once the symptoms started and it didn't fix the issue.  Probably not the best method for diagnosis, but the way i finally confirmed it was my TC was by adding a friction modifier additive to my trans fluid that actually fixed the problem for about a month before the symptoms returned.  The results were immediate, so i knew it was trans/tc related.

Had the trans rebuilt and got a new converter put in about a year ago.  It's recommended to get the whole thing rebuilt when you do a TC or the problems can just come back because of possible contamination.  Been good ever since.